var xPos = 300;
var yPos = 200;
var step = 1;
var delay = 100;
var height = 0;
var Hoffset = 0;
var Woffset = 0;
var yon = 0;
var xon = 0;
var pause = true;
var interval;
img1.style.top = yPos;
function changePos() {
    if (navigator.appName == "Microsoft Internet Explorer") {
        if (navigator.appVersion.match(/7./i) == '7.') {
            width = document.body.clientWidth-400;
            height = document.body.clientHeight-300;
        } else {
            width = document.body.clientWidth;
            height = document.body.clientHeight+400;
        }
    }
    Hoffset = img1.offsetHeight;
    Woffset = img1.offsetWidth;
    img1.style.left = xPos + document.body.scrollLeft;
    img1.style.top = yPos + document.body.scrollTop;
    if (yon)
    { yPos = yPos + step; }
    else
    { yPos = yPos - step; }
    if (yPos < 0)
    { yon = 1; yPos = 0; }
    if (yPos >= (height - Hoffset))
    { yon = 0; yPos = (height - Hoffset); }
    if (xon)
    { xPos = xPos + step; }
    else
    { xPos = xPos - step; }
    if (xPos < 0)
    { xon = 1; xPos = 0; }
    if (xPos >= (width - Woffset))
    { xon = 0; xPos = (width - Woffset); }
}

function start() {
    img1.visibility = "visible";
    interval = setInterval('changePos()', delay);
}
function pause_resume() {
    if (pause) {
        clearInterval(interval);
        pause = false;
    }
    else {
        interval = setInterval('changePos()', delay);
        pause = true;
    }
}
start();